How to get prepared for NDA exams with just 3 months of time?

Sir, i am a class 12th student in science stream. My h.s. Exam. Is nearby.
I want to also join the indian air force academy. I want to give the NDA exams but my preparation is nothing for the NDA exams and jst 3 months i have time for this exam. Now between this 3 months what should i do or which books i follow for better rank in this exam?